1. Field
The disclosed concept pertains generally to direct current power sources and loads, and, more particularly, to power flow regulators for direct current power sources and loads.
2. Background Information
In most solar systems, for example, a relatively large number of solar strings are electrically connected in parallel, which forces all of the string voltages to be identical. However, the optimal operating voltage of each solar string might not be the same in terms of maximum power extraction. The differences between the optimal operating voltages are typically relatively small (e.g., without limitation, less than about 20 VDC). Such parallel solar strings can lower the overall system efficiency by up to about 15%.
As shown in FIG. 1, multiple parallel connected DC sources 2,4,6 are used to supply a DC load 8. One example of such a system is multiple DC solar strings supplying one DC load or supplying a DC link of a solar inverter.
Similarly, one DC source 10 can supply multiple DC loads 12,14,16 as shown in FIG. 2. One example is that one DC source can charge multiple parallel connected batteries.
Combining FIGS. 1 and 2 together, multiple DC sources 18,20,22 can supply multiple DC loads 24,26,28 as shown in FIG. 3.
When the multiple parallel connected DC sources 2,4,6 supply the DC load 8 of FIG. 1, in some cases, a DC source's output power is determined by its DC voltage, such as the voltage of a solar panel (string). In FIG. 1, the source voltages of the DC sources 2,4,6 are always equal to the load voltage of the DC load 8. The output power of the individual DC sources 2,4,6 is determined by the DC load voltage. It is impossible to change DC power distribution among the DC sources 2,4,6 since this is solely determined by load voltage.
When the multiple parallel connected DC loads 12,14,16 are supplied by the DC source 10 of FIG. 2, in some cases, a DC load's power is determined by its DC voltage. In FIG. 2, the load voltages of the DC loads 12,14,16 are always equal to the source voltage of the DC source 10. The consumed power of the individual DC loads 12,14,16 is determined by the DC source voltage. It is impossible to change DC power distribution among the DC loads 12,14,16 since this is solely determined by source voltage.
When the multiple parallel connected DC sources 18,20,22 supply the multiple DC loads 24,26,28 of FIG. 3, if a DC source's output power is determined by its DC voltage, it is impossible to change DC power distribution among the DC sources 18,20,22 since this is solely determined by load voltage. If a DC load's power is determined by its DC voltage, then it is impossible to change DC power distribution among the DC loads 24,26,28 since this is solely determined by source voltage.
There is room for improvement in power flow regulators.